First report of interspecific facultative social parasitism in the paper wasp genus Mischocyttarus Saussure (Hymenoptera, Vespidae). Parasitism of colonies of the social wasp Mischocyttarus cerberus Ducke, 1918 by females of Mischocyttarus consimilis Zikán, 1949 was observed in a rural area of Dourados, state of Mato Grosso do Sul, Brazil. In all monitored cases, the invasion occurred in the pre-emergence colony stage, generally by a single female of M. consimilis. The period of establishment of the foreign female in the host colony was marked by antagonistic behaviors between the host female and the invasive. In general, the architecture of the parasitized nest was modified from the typical architecture of the host species nest.

Facultative social parasitism involving the invasion of a queenright colony by a foreign reproductive female has been documented in all three subfamilies of social wasps in the family Vespidae (Taylor 1939; Wilson 1971). In the subfamily Polistinae specifically, intraspecific facultative social parasitism has been described in both the genera Polistes Latreille, 1802 (Strassmann 1981; Klahn 1988) and Mischocyttarus Saussure, 1853 (Litte 1979); whereas interspecific facultative social parasitism has been described only in the genus Polistes (O' Donnell & Jeanne 1991; Giannotti 1995; Cervo & Dani 1996; Cervo et al. 2004). A single case of interspecific interaction in the genus Mischocyttarus was recorded by Pinto et al. (2004), in which two females coexisted in the initial phases of colony development. Here we provide the first report of the phenomenon of interspecific facultative social parasitism in the paper wasp genus Mischocyttarus.

Mischocyttarus cerberus Ducke, 1918 is a neotropical social wasp that occurs in central-western and southeastern Brazil. Colonies of M. cerberus are generally founded by a single female, and nests consist of one uncovered comb, which is attached to the substratum by a single peripheral petiole (Fig. 1A) (Giannotti 1998, 1999). Similarly, Mischocyttarus consimilis Zikán, 1949 is a neotropical social wasp, which until recently was known only from Paraguay but has now been reported from central-western Brazil. Relatively little is known about its life-history; the first studies were carried out only recently. Colonies of M. consimilis are generally founded by a single female, and nests consist of one uncovered comb, which is attached to the substratum by a single centralized petiole (Fig. 1B) (Montagna et al. 2010; Torres et al. 2011). Individuals of M. consimilis closely resemble individuals of M. cerberus in their body size and color pattern (Fig. 1). In agreement with Ortolani et al. (2010) the morphologic similarity among two species should motivate the parasitism for the invader species.

Parasitism of colonies was observed under field conditions in the municipal district of Dourados (22º13'16"S; 54º48'20"W), state of Mato Grosso do Sul, Brazil. The climate of this region, according to Zavatini (1992), is humid subtropical, with higher precipitation and temperatures in September through February (warm-rainy season), and less precipitation and mild temperatures in March through August (cold-dry season). All the parasitized colonies, located in a rural area, were monitored weekly from March 2010 through June 2011. Within an area of approximately two hectares, all cases of parasitism of colonies of M. cerberus were recorded. This location has low human presence and predominantly arboreal vegetation. All the parasitized colonies were attached to the edges of roofs of old outbuildings and vacant houses.

The events of parasitism of colonies of M. cerberus by females of M. consimilis were observed during both climate seasons. We recorded 11 cases of parasitism during the study period, but monitored only five parasitized colonies from the beginning of the parasitism until the colony declined. All the monitored colonies were founded by haplometrosis, and were in pre-emergence when the invasion occurred (17.2 ± 8.2 cells; mean ± SD; n = 5) (Fig 1C). Four colonies were invaded by a single female, and the other was invaded simultaneously by three females of M. consimilis. Giannotti (1998) demonstrated that most of the colonies of M. cerberus are founded by haplometrosis, and this behavior may have favored the invasion by females of M. consimilis observed in this study. In general, colonies founded by haplometrosis have low potential defenses against invaders compared to those founded by pleometrosis (Gamboa 1978; Gamboa et al. 1992).

The invasion and the period of establishment of the foreign female in the host colony were marked by antagonistic behaviors between the host and foreign females, mainly combat with attacks in the form of bites and lunges. The conflict period lasted three to five days, and during this period the host female dedicated most of her time to attempting to expel the foreign female. Subsequently, the aggressive behaviors gradually decreased and the host and foreign females began to coexist in the colony. Previous studies with social wasps of independent-foundation have demonstrated that the invader female must develop several strategies to attain success in the invasion, for instance acting more aggressively (Cervo & Lorenzi 1996; Cervo et al. 2004), or still more complex strategies such as mimicking the chemical signature of the host colony (Lorenzi et al. 2004; 2007). Queens of both species divided their reproductive activities equally, and the first offspring of M. consimilis emerged after a mean period of 75.2 ± 6.3 days (mean ± SD; n = 5). The individuals of the two species that emerged during the remaining colony's cycle shared equally in the maintenance of the host colony, confirming this phenomenon as facultative social parasitism (Taylor 1939).

The architecture of all the old parasitized nests differed from the typical architecture of the host-species nest. Giannotti (1999) described an elongated comb and peripheral petiole for the nest of M. cerberus, and Montagna et al. (2010) described an elliptical comb and centralized petiole for the nest of M. consimilis. Old parasitized nests had the peripheral petiole typical of the host species; however, the combs were elliptical, similar to those constructed by the invader species (Fig. 1D). This suggests that the tasks of constructing the nest were shared among the offspring of the two species.

ACKNOWLEDGMENTS

The authors thank Orlando T. Silveira (Museu Paraense Emílio Goeldi) for the identification of the species and Janet W. Reid (JWR Associates) for the revision of the English text. CAPES provided a doctoral fellowship to the first author, and WFAJ acknowledges his research grants from the CNPq.

Giannotti, E. 1995. Notes on an occurrence of interspecific, facultative temporary social parasitism between two species of Polistes from Brazil (Hymenoptera: Vespidae). Revista Brasileira de Entomologia 39: 787-791. [ Links ]